Ammonium nitrate and urea explosives



United States If atent 2,814,555 Patented Nov. 26, 1957 1 2,814,555 AMlVIONIUM NITRATE AND UREA EXPLOSIVES William H. Rinkenbach, Salisbury Township, Lehigh County, and William J. Carroll, Jr., Allentown, Pa., assignors to Trojan Powder Company, a corporation of New York No Drawing. Application May 18, 1955, Serial No. 509,395 2 Claims. (Cl. 52-14) This invention relates to blasting explosives of the nongelatinized type in which ammonium nitrate and urea crystals are the chief constituents.

The invention provides an explosive that shows maximum explosive force and dependable detonation under conditions of use. The explosive force in fact is greater with the admixed urea than for the ammonium nitrate alone.

When ammonium nitrate and urea are well mixed and allowed to stand, as in an explosive in storage, the contacting particles undergo some bonding at their interfaces. This bonding is considered to be due to possibly solid difiusion or solution, with the production of a very thin film of low melting eutectic of the two materials. Whatever the exact mechanism of the change may be, the invention provides also means of overcoming this difficulty.

Briefly stated, the invention comprises an explosive mixture of fine ammonium nitrate and urea crystals, the urea being in the proportion of 16-21 parts for 100 of the total explosive. In the embodiment giving the least deterioration in storage, the invention comprises such explosive intimately mixed with a few percent of a powdered absorbent for liquid, to decrease bonding between contacting particles of the urea and ammonium nitrate.

Products so made are safe in handling yet detonatable under confinement by a No. 16 blasting cap. On an equal weight basis, they have the explosive power of 50% dynamite. Their standard (unpacked) density varies from about 0.93 to 0.99.

The principal reaction occurring at the time of the explosion may be represented as follows:

The molecular proportions shown are the stoichiometric for giving oxygen balance between the oxidizing material (the nitrate) and the combustible urea.

While the proportions for exact oxygen balance are 80 nitrate by weight for 20 of urea, we obtain the desired explosive power when the proportion of urea is within the range 16-21 parts.

Both the urea and the ammonium nitrate used should be in the form of crystals of size to pass substantially completely through a mesh screen and to be retained to the extent of at least 50% on 200 mesh.

The absorbent of liquid introduced to retard and (for practical purposes prevent) bonding between the contacting surfaces of the urea and nitrate particles is present in very limited proportions and is thoroughly mixed throughout the whole composition. Thus it may constitute l%-3% of the weight of the explosive mixture. When used in such low proportion, the amount of urea is so selected within the range 16-21 parts that the amount of ammonium nitrate used is that required for approximate oxygen balance and makes the total weight 100 parts.

The absorbent for liquid should be stable, powdered or finely divided as used, and chemically inert in storage in contact with the urea and ammonium nitrate. It must be absorbent of moderate amounts at least of liquid, particularly urea-nitrate mix, without liquefaction or bonding so as to maintain a dry condition at the interfaces between the urea and nitrate particles. Examples of materials that meet the requirements for the absorber and illustrate the class of materials to be used are the powdered earthy materials such as clay, kaolin, diatomaceous earth, and fullers earth. Other examples are rosin, methyl cellulose, and like resins and cellulose ethers. When such absorbent is combustible, the proportion of ammonium nitrate is increased moderately, to maintain approximate balance between combustible and oxidizing components so that the nitrogen in the gaseous explosion products appears in elemental form. When the absorbent is chemically inert during the explosion, as in the case of the earthy absorbents, there is no significant decrease in the explosive power per unit weight of the actual explosive mixture and also no requirement for extra ammonium nitrate.

The invention will be further illustrated by description in connection with the following specific examples of the practice of it. In these examples and elsewhere herein proportions are expressed as parts by weight except where specifically stated to the contrary.

Example 1 790 g. of crystalline ammonium nitrate and 210 g. of urea were mixed thoroughly and passed several times through a number 10 sieve. The crystals of the nitrate and also of the urea were of size to pass substantially completely through 10 mesh and to be retained to the extent of at least 50% on 200 mesh. In the ballistic pendulum test with a No. 16 blasting cap, complete detonation took place. 10 g. of the mixture had the explosive power of 10.7 g. of TNT. When tamped into a steel pipe, the mixture detonated at the rate of 2,958 meters per second.

Example 2 810 g. of crystalline ammonium nitrate of kind described, 160 g. of urea, and 30 g. of colloidal kaolin as absorbent of liquid were mixed as described under Example 1. The resulting mixture was found to withstand interparticle bonding and segregation when stored. It was a powerful explosive.

Example 3 The procedure of Example 2 is followed, with the substitution of any of the absorbents of liquids disclosed herein for the kaolin, on an equal weight basis.

It is to be understood that it is intended to cover all changes and modifications of the examples of the invention herein chosen for the purpose of illustration which do not constitute departures from the spirit and scope of the invention.

What is claimed is:

1. A blasting explosive consisting essentially of mixed crystals of ammonium nitrate, crystals of urea, and a dry pulverulent absorbent for liquid thoroughly mixed with the said crystals, both the ammonium nitrate and urea being in the form of solid particles of size to pass substantially completely through a IO-mesh screen and to be retained to the extent of at least 50% by Weight on 200 mesh and the proportions of the materials being 16-21 parts by weight of urea and 13 parts of the absorbent for total weight of the urea and ammonium nitrate.

2. The blasting explosive of claim 1 in which the said absorbent is a powdered material selected from the group consisting of clay, kaolin, diatomaceous earth, and fullers earth.

References Cited in the file of this patent UNITED STATES PATENTS 1,028,950 OBrein June 11, 1912 2,129,367 Williams et a1. Sept. 6, 1938 2,353,137 Cook et a1. July 11, 1944 2,398,071 Barab Apr. 9, 1946 2,455,205 Whetstone et al. Nov. 30, 1948 

1. A BLASTING EXPLOSIVE CONSISTING ESSENTIALLY OF MIXED CRYSTALS OF AMMONIUM NITRATE, CRYSTALS OF UREA, AND A DRY PULVERULENT ABSORBENT FOR LIQUID THOROUGHLY MIXED WITHH THE SAID CRYSTALS, BOTH THE AMMONIUM NITRATE AND UREA BEING IN THE FORM OF SOLID PARTICLES OF SIZE TO PASS SUBSTANTIALLY COMPLETELY THROUGH A 10-MESH SCREEN AND TO BE RETAINED TO THE EXTENT OF AT LEAST 50% BY WEIGHT ON 200 MESH AND THE PROPORTIONS OF THE MATERIALS BEING 16-21 PARTS BY WEIGHT OF UREA AND1-3 PARTS OF THE ABSORBENT FOR 100 TOTAL WEIGHT OF THE UREA AND AMMONIUM NITRATE. 